Same-sex sexual behaviour among non-human primates may help reinforce social bonds and maintain group stability during environmental or social stress, according to new research. Writing in Nature Ecology & Evolution, scientists analysed reports across 59 primate species, including chimpanzees, Barbary macaques and mountain gorillas, finding the behaviour to be widespread.
The study, co-authored by Prof Vincent Savolainen of Imperial College London, suggests the behaviour either has deep evolutionary roots or evolved independently multiple times. Researchers found it was more common in species living in harsher, drier environments with scarce resources and higher predation risk. It was also linked to longer lifespans, pronounced size differences between sexes, and complex social hierarchies.
Lead author Chloe Coxshall said environmental influences on such behaviour had often been overlooked despite evidence of heritability. The team argues same-sex interactions may reduce aggression, ease tension and strengthen cooperation, helping groups navigate challenges. While cautioning against direct comparisons with humans, the researchers noted early human species likely faced similar pressures. Independent experts welcomed the findings as evidence that same-sex behaviour is a common and adaptive feature of primate societies, while also stressing that human sexuality is shaped by far more complex factors.
